Separation of different melting point materials



Sept. 22, 1942. Y A. H. SCHUTTE 2,296,4

SEPARATION OF DIFFERENT MELTING POINT MATERIALS Filed Sept. 20, 1941 INVENTOR v Hwy 6' Patented Sept. 22, 1942 SEPARATION OF DIFFERENT MELTING POINT MATERIALS August Henry Schntte, Hastings on Hudson, N. Y.

Application September 20, 1941, Serial No. 411,646

9 Claims.

terials from mixtures thereof and more particu-- larly to the concentration of higher melting point materials from lower melting point materials in a mixture thereof. It is, in a sense, a fractional solidification and separation by the aid of an emulsion whereby separation is facilitated. It is a continuation-in-part and modification of the invention disclosed in my copending application, Ser. No. 274,412, filed May 18, 1939, and entitled Separation of difierent melting point materials.

As set forth in the foregoing application, I have discovered that I can obtain a highly effective separation of mixtures of materials having different melting points by forming an emulsion of such a mixture with a non-solvent fluid and thereafter cooling th emulsion to such a temperature that one of the materials to be separated becomes filterable or separable by liquid-solid separation from the other. The non-solvent fluid surrounds the crystals or solid particles and the liquid particles and produces a free-filtering, free-draining, and free-settling system. I then separate the liquid from the solid material and thereafter separate out the nonsolvent fluid It is well known that vegetable oils such as soybean oil are mixtures of the glycerides of higher fatty acids, som of which are saturated and some of which are unsaturated. The glyc-' erides of the more unsaturated acids, particularly linoleic and linolenic acids, are valuable as drying oils; they have melting points that are comparatively low and are below the freezing point of water. The glycerides of other acids such as palmitic and stearic acids, which are saturated, and oleic acid have a much higher melting point and are commercially known as the saturated or non-drying oils and are useful primarily in the production of soap.

A typical approximate analysis of a mixture of soybean fatty acids as described in "Chemical and Metallurgical Engineering, volume XLII, No. 9, September, 1940, page 618 is as follows:

The melting points of the several fatty acids above referred to are taken from Pen'ys Chemical Engineers Handbook (1934 edition).

Th separation of the relatively more saturated and relatively more unsaturated fatty acids or fatty acid glycerides from a mixture thereof is of considerable importance from the commercial standpoint in order that'the objectionable qualities of one group do not influence the highly desirable qualities of the other group. In the past, such separation has been accomplished principally by distillation procedures; however, partial decomposition of the fatty acids or their glycerides occurs at the high temperatures required, and it has been found difiicult to accomplish a sharp fractionation. Solvent fractionation of such materials has also been proposed, but attempts in this respect have not been entirely satisfactory.

The principal object of my invention is to effeet a separation of a mixture of higher fatty acids or their glycerides into the relatively more saturated and the relatively more unsaturated constituents by forming an emulsion of the mixture and accomplishing a liquid-solid separa tion of the emulsion after cooling.

A more specific object of my invention is to fractionally separate a mixture of the saturated and unsaturated fatty acids and their derivatives obtained from soybean oil by forming a free-filtering emulsion of the mixture in which the higher melting point compounds, which are relatively saturated, are solidified.

In accordance with the Preferred form of embodiment-of my invention as shown on the attached drawing, which represents a general or typical flow sheet, it will be noted that I provide a tank it for receiving a mixture of fatty acids or their glycerides obtainable, for example, from soybean oil. Preferably, this tank is provided with a source of heating medium such as steam, which is conveniently introduced through line it into jacket 82 to maintain th mixture in a liquid condition. It is to be understood that, for the purposes of my invention, the material may be either the soybean oil itself or a mixture of the fatty acids characteristic thereof.

A supply of a suitable non-solvent liquid is maintained in tank it, which is preferably jacketed as at it and is maintained at a predetermined temperature by mean of the heating medium introduced through line It, Preferably both materials are maintained at substantially the same temperature, and the condensate from the steam jackets is withdrawn through the lines it.

Water is the preferable non-solvent liquid for forming the emulsion with the soybean fatty acids. Other liquids such as aqueous salt solutions or low boiling organic liquids may be selected; but it is preferable that the emulsifying material should form a suitable emulsion with the fatty acid materials and should have no substantial solvent or chemical effect thereon. I

have found water satisfactory with the soybean acids, and reference will hereafter be made to this as the emulsifying material,

Predetermined quantities of the non-solvent liquid and the mixture of fatty acidmaterials are drawn off through lines and 2, respectively, by the proportioning pump 22, and the streams are consolidated in the manifold24 and introduced into mixer 26. This mixer may be any suitable type of emulsifier or homogenizer, but I find that in many cases a rotary pump is'adequate if provided with a by-pass 21 and 'a relief valve 28. It will be appreciated that,'by adjusting the capacity of the mixer 2'6, it will be possible to recycle the material through the mixer as .many times as may be desirable so that the resulting material discharged through line 30 is suitably emulsified. I usually find it preferable to add an inert, non-solvent gas through line 34 to the mixture in manifold 24 to aerate or otherwise expand the emulsion, and in some cases I can use the gas to the exclusion of the liquid non-solvent. 1 prefer to directly cool the emulsion as by the direct introduction of a coolant at 32 into the by-pass line 21 wherethis is possible; otherwise, indirect cooling may be applied satisfactorily. Both direct and indirect cooling may be used if desired. Where direct cooling is used, it is frequently desirable to select as the cooling medium a nonreactive emulsifying material such as that contained in tank l4,

Having established a suitable emulsion with a large interfacial area between the crystallized material and the non-solvent, I am able to obtain a very high rate of separation in the liquid-solid separator 36. Although this is indicated as a centrifugal type, it may be either a centrifugal filter having a foraminous filter basket, or it may be a clarifler with a solid bowl. It is, of course, in the'contemplation of my invention that the separator, the primary function of which is to separate liquids from solids, may be any desired type including a pressure or a vacuum filter of the continuous or other type and having filter discs or a drum as may be desired. In some cases gravity settling may be practiced.

In the preferred form of embodiment of my in vention and particularly for economical high speed operation, I find a centrifugal basket filter having a perforated rotating basket lined on the interior with a foraminous filtering medium to be most effective. This is rotated at such a speed that a high separating force, which may be in the range of 500 to 1,000 times gravity or more, is obtained.

The cake formed is normally a' fine-grained, free-filtering, porous type; and, inasmuch as the filteringforce is gravitational bynature, the entire cake is submitted t the filteringforce without an external pressing action. It is, of course, possible and usually desirable to wash such cake with a wash liquid as from line 38. Such wash liquid will readily permeate the cake. A uniform washing and drying of the cake are thus possible. The wash liquid may be either a diluent for the liquid material of the emulsion or a liquid which is inert with respect thereto and a non-solvent therefor. An inert and non-solvent wash liquid does not dilute the liquid part of the emulsion and yet serves as a suitable displacing medium which is especially effective where the solid part of the emulsion is porous as in the instant case.

With the proper temperature control, the liquid unsaturated fatty acid material that is separated from the saturated fatty acid material filter cake is withdrawn through the line 40 into tank 42 provided with a suitable heating jacket 43. The unsaturated low melting point fatty acid material is removed through the line 44.

The wash liquid filtrate may be withdrawn through the line 46 by suitable manipulation of the valves into tank 48 provided with jacket 48. This filtrate may be either recycled through linev 55 by means of the pump 56 or otherwise discharged as through the line 54. It will be understood that tanks 42 and 48 are maintained at the desired temperature by the introduction of a heating medium at 50 and the discharge thereof at 5 The filter cake, which is the higher melting point material, maybe removed from the separator 36 and collected in the tank 51, which is also provided with a heating jacket 58, to which a heating medium is supplied at 59 andfrom which the heating medium is removed at 60. The saturated, high melting point fatty acid material is removed through line 6|.

As an example of the operation of my invention on soybean acids, an emulsion of soybean fatty acids having a melting point of 64 F. and an iodine number (Wijs) of 137.5 was made with water. Equal parts of water and acids were used, and the resulting emulsion was chilled as indicated on the following table: I

Run No.

Filtering temp -F- 70 50 45 Cake: u

Iodine number (W 11s) 82. 3 87. 2 111. 2 129. 3

Melting point F 105 101 82 71 Cloud point--- -F- 180 144 Yield wt. 12. 5 19. 5 39 77 Filtrate:

Iodine number (Wijs) 144. 9 149. 3 155 155 Melting point F 52 46 28 23 Cloud point. 155 137 Yield 87. 5 80. 5 61 23 In a once-through operation without washing, it was possible to obtain a filtrate having an iodine number of 149.3 with an 80.5% yield or a filtrate having an iodine number as high as 155 with only a somewhat smaller yield. With a recycle ratio of filtrate to initial charge of two or three to one and with suitable washing with a non-solvent wash liquid, it is possible to obtain substantially theoretical yields.

' The separation of soybean oil into fractions comprising respectively the relatively more saturated and the relatively more unsaturated constituents thereof can also be effected by my process. The soybean oil is emulsified with water for example, and the resulting emulsion is chilled to such a temperature that a portion of the soybean oil solidifies. 'Upon separation in a suitable manner, a filter cake comprising the relatively more saturated constituents and a filtrate comprising the relatively more unsaturated consti- 

